Thumb-suckers and nail biters may get fewer allergies

Young children who suck their thumbs or bite their nails may be less likely to develop allergies later in childhood, a new study claims.

Babies have been seen sucking on their fingers in uterus weeks before birth, but the sight of an older child with their fingers in their mouth can drive parents crazy, bringing up fears about everything from social stigma to germs. But according to new research, those habits in children aged five to 11 may indeed increase exposure to microbes, but that might not be all.

A long-ranging study of more than 1000 children in Dunedin, New Zealand, followed their lives from age five to 13 to 32, using skin-prick tests to determine allergy sensitivity.

The results showed that 49 per cent of children who didn't suck their thumbs or bite their nails had developed an allergy by age 13, compared to 38 per cent of children who did.

What's more, the kids who both bit their nails and sucked their thumbs had an even lower risk of allergy with 31 per cent testing positive. When they were again tested at 32, the allergies remained the same.

Study lead author Professor Bob Hancox said the exposure through thumb-sucking may alter immune function so that children with these habits become less prone to developing allergy.

"The findings support the 'hygiene hypothesis', which suggests that being exposed to microbes as a child reduces your risk of developing allergies," he said.

Despite these findings, Professor Hancox and his co-authors do not suggest that children should be encouraged to take up these habits, because it is unclear if there is a true health benefit.

Stephanie Lynch, a medical student who collaborated on the study, added that although thumb-suckers and nail-biters had fewer allergies on skin testing, the researchers found no difference in their risk for developing allergic diseases such as asthma or hay fever.

The study results were first published in the U.S. journal of Pediatrics.